Automatic voltage regulating circuit



May 23, 1,961 L. F. BIRD AUTOMATIC VOLTAGE REGULATING CIRCUIT Filed Jan."F, 1958 MWE/c +5 FORCE United States Patent C 2,985,817 AUTOMATICVOLTAGE REGULATING CIRCUIT Lester F. Bird, Newark, NJ., assignor toEngelhard ovm, Inc., a corporation of New Jersey Filed Jan. 7, 1958,Ser. No. 707,495 Claims. (Cl. 323-56) The present invention deals withan automatic voltage regulating circuit and more particularly to anautomatic voltage regulating circuit that will deliver steady andunvarying voltage to a connected load from supply voltages that varyeither above or below a normal value.

It is yan object of the invention to provide a voltage regulator whichutilizes power from a supply line at high power yfactor and higheiciency. It is another object of the invention to provide a lvoltageregulator having a minimum of energy storage in the component partsthereof. It is a further object of the invention to provide a voltageregulator which has minimum disturbances or transients in its outputvoltage regardless of sudden alterations or fluctuations in supply linevoltage. Other objects and advantages of the invention will becomeapparent from the description hereinafter following and the drawingsIforming a part hereof, in which:

Figure 1 is a schematic illustration of a regulator circuit according tothe invention,

Figure 2 is a graphic illustration of a hysteresis loop for the ironcomprising the core of the transformer, and

Figure 3 is Ia graphic illustration of the performance of the regulatorcircuit showing steady output voltage against variable input line supplyvoltage.

The invention deals with a regulator circuit comprising a particulartransformer structure and associated Windings, which, together with aconventional type reactor and capacitor constitute suicient structurefor providing the delivery of unvarying voltage to a load when the inputvoltage varies above and below the normal voltage value. The regulatorcircuit has at least two major improvements over the usual magneticvoltage stabilizers, including a minimum of bulk and a comparativelyshort recovery time lfrom the effects of transients in the supplyvoltage.

Referring to Figure l, supply lines 1 and 2 are of xed frequency andvarying voltage. They are connected to the primary Winding of a threelegged autotransformer 3 having in series with line 1 a series reactor4. The transformer 3 has a divided primary winding 5 and 5 and a dividedsecondary winding 6 and 6. The windings 5 and 5 are poled to producemagnetic flux which is additive in the peripheral magnetic core loop andwhich produces substantially no net flux in the central leg of the core.The windings of transformer 3 are mounted upon a closed type of magneticcore structure 7 of thin laminated steel. A separate coil 8 is mountedupon the middle leg of the core structure. A capacitor 9 is connectedacross a portion of the split secondary coils. For purposes ofillustration the output leads 10 and I11 are shown connected to a powerconsuming load 12. It is possible to deliver power to the load 12 fromthe magnetic core structure either by magnetically induced windings orthrough capacitative or other coupling arrangements.

Reactor 4 may be air or iron core design and should have a reactancethat is not altered by normal current variations occurring lfromoperation of the circuit.

It is not necessary that the trans-former be of the auto type since theinput windings may be wound separate from the secondary windingsaccording to well known practice.

Figure 2 illustrates a diagrammatic hysteresis loop for the core iron.The instantaneous ux densities are plotted along the vertical axes -i-Hand -H and the magnetic forces along the horizontal axes +B and -B.

Since voltage across a coil wound upon such a core follows closely thechanges in magnetic flux through it the voltage can be assumed to beequivalent to the maximum vertical height of the hysteresis loop. Anyfactor that is introduced altering the height of the loop automaticallyalters the developed voltage. Changes in the amount of iron in the coreis such a factor and a removal of a portion of the iron will reduce therange of possiblev flux change, which is equivalent to the removal ofthe area C of the hysteresis loop.

Because there are definite limits to the flux that can be carried by theiron, the introduction of flux from an external source will reduce theflux change available to the regular source and reduce the possiblevoltage across the coil. The addition of this external flux has the sameeffect as the reduction in quantity of core iron.`

lt is possible therefore to control the voltage across the coil by theaddition and subtraction of magnetic flux from an external source. v

The auxiliary winding upon the transformer core of the invention is suchan independent source of flux to the transformer core and is abletherefore to control the voltage of the coil. By connecting thisauxiliary winding back to the supply voltage a result is achieved inwhich the voltages of the transformer coils are subject in some measureto variations in the supply line voltages.

Figure l illustrates a circuit having a supply voltage source, a seriesreactor, a transformer, a capacitor and a power consuming load. Thetransformer is normal except for the yform of the core structure. If thetransformer is assumed to be ideal in its properties the cir-v p formerand the capacitor are assumed to lact as if they were a capacitor of anadjusted value.

For convenience, the reactance of an inductance is consideredalgebraically as a positive quantity. The reactance of a capacitor isconsidered to be negative. In such a series circuit these reactances areadded algebraically to determine the total reactance of the circuit. Ifthe algebraic sum of these reactances should be a low figurel therewould be but little impedance to limit the flow of current. As a resultthe currents would become very large and the voltages across the circuitelements rise to high values.

In the circuit of the invention, however, the capacitor is shunted bythe windings of the transformer. The possible voltages that can bedeveloped by the capacitor are limited by the restrictions imposed bythe voltage handling abilities of the transformer coil.

As the impressed voltage across the transformer is increased, themagnetizing currents are increased and, as a condition of saturation isapproached in the core iron, these currents increase rapidly withincreasing voltage.

The magnetzing currents are of essentially opposite phase to the normalcapacitative currents and have the effect of reducing the effectivevalue of the capacitor.

In the series circuit a reduction in the value of the capacitorautomatically increases the circuit reactance and reduces the current. Acondition of balance is produced in the system Where the currents andthe changing reactances are stabilized. The voltages across thecapacitor and transformer coil are stabilized at the same time with onlya small variation in capacitor voltage remaining as a result of linevoltage changes. The capacitor volt- Patented May 23, 1961agestillincreases slightly with increasingwline voltage and fallsslightly with -falling line voltages.

It is necessary if the output voltage is constant and independentof rthevariations insupply line yvoltage that someradditional featurefbe addedto the-systemito eliminate the small changes in voltage across thecapacitor. I "have fprovided i such ya `feature in fthe yauxiliary`winding across the middle lleg of the transformer .core.

The auxiliary windingis connected 'back `to :the supply line voltage-and therefore 4its currents `and -voltage `vary with thatofthe line.The magneticfeffects of the winding appear in the -ux of fthe coreingopposition to the mainilux. At thetirne when thecapacitor lvoltagewould normally'rise dueto increasing line lvoltage thefcurrents in-theauxiliary winding :areincreased and the resultant flux increases 1 thesaturation alternatelyriirst in one and then-inthe otherofthetwolouter'legs of thettransformer. Thiseliminates the expectedchange'incapacitor voltage. Likewise, lif `the f supply voltage |isdecreased .and a 4fall in capacitor voltage might result, the `liux fromthe auxiliary winding `is reduced and eliminates the expected changefrom the capacitor voltage. It is possible by `this inventionto have theoutput voltage remain constant and unaffected by variations occurring inthe supply voltages. Whenl a sudden `transient causes an abrupt changein the supply voltage the usual `magnetically controlled voltageregulator permits `a transient to pass through to the load circuit. Theseverity and duration `of this transient varies with the construction ofthe regulatorbut is cornmonlyof Afrom seven to twenty ,cycles in lengthbefore the -output voltage is yagain in a steady state. With the circuitvof 4theirrvention this recovery time is materially shortened and vtheamplitude of the transient reduced. The reason *for this performancelies inthe use Vof Ythe auxiliary 'Winding connected to the supply line.The transient is applied to the core of the transformerfrombothfdirections simultaneously and, as a result it is cancelled-out `ofthe capacitor voltage.

Various modiiications `of the invention are contemplated within the-scope of the appended claims.

' What is v'claimed is:

l. An 'automatic `voltage regulatingcircuit comprising a'transformerhaving a closed-type three-legged core, the legs -being spaced `fromeach other, primary and `secondary windings on the outer legs of saidcore, input leads connected to said primary windings, 'a series reactorin at least one Aof said leads,output leads connected to said secondarywindings, a load and capacitor connected across'said secondary leads inparallel relationship, an

claim .1, `-wherein.said.primaryand. secondary .windings .areautotransformer windings on each of said outer legs, the primarywindings being electrically connected to each other.

3. In combination, a magnetic core including rst and second magneticloops having a common portion, primary and secondary windings Vmountedon the individual portions of said fir-st .and secondloopsmeans-for-energizing said primary windings `from a source of alternating currenttoproducemagnetic fluxiinthe saturation region in the individualportions-of said rst and second magnetic loops andtoprovide.substantiallyzero,magnetic flux in the common portion of saidmagnetic'loop, an auxiliary coil mounted-on.theccommontportion of saidcore, and means for energizing said auxiliary coil from the same sourceof alternating current which is energizing said primary windings.

v4. A regulation circuit vcomprising a magneticlcore including iirst andsecond magnetic loops having a Icommon portion, primary windingsmounted-on the individual portions of said Vrst andsecond magneticloops, means for energizingsaid primary windings :from asource ofalternating current toproduce magnetic flux in the saturation region intheindividual.portionsof said rst and-second magnetic loops and Vtoprovide substantially `zero magnetic tlux in the .common portionfofzsai'd magnetic loop, an lauxiliary winding mounted on the common'portion of said core, -andzmeansffor.energizing said auxiliary coilrfrom thesame source of alternating currentwhich is :energizingsaidprimary windings.

5. An automatic yvoltage regulating circuit comprisingfa magnetic core.including first and second :magnetic loops having a common portion,primary iandfsecondary windings mounted. on the `individual portionsofsaid iirstf'and second magnetic loops, `means yfor 'energizing saidprimary windings -from a source of alternating icurrent vto producemagnetic flux vin the saturationregion :in the I individual portions ofsaid first and vsecond;magnetic,loops auxiliary winding on Ythetransformer `leg between said outer legs, land Ymeans Jfor applyingalternating current power signals to said auxiliary winding.

2. An automatic voltage lregulating circuit according to and to providesubstantially 4zero magnetic ux in the common `portion of said magneticloopyan auxiliary winding mounted on theicommon portion oftsaid core,means for energizing vsaid auxiliary .coil `from. `.the same source ofalternating rcurrent which is energizing said primary windings, avreactor connected'in series with Aone `of said primary windings, andaload and capacitor v,connected to said ysecondary windings.

lReferences Cited in the tile of this patent UNITED STATES PATENTS2,338,080 Brown Dec. 28, "i943 '2,399,185 VHedding Apr. 30, 19462,481,644 Callaway Sept. 13, :1949

